Method for preparing a roller dried protein preparation

ABSTRACT

The invention relates to a method for preparing a dried protein preparation, comprising roller drying a protein solution having a relatively low protein content of less than 40%, wherein the proteins in the solution are intermolecularly crosslinked by covalent bonds, for example by means of enzymatic treatment, such as with transglutaminase.

[0001] The present invention relates to a method for preparing a driedprotein preparation.

[0002] The preparation of protein powders can for example be achieved bymeans of spray drying. Spray drying can be effected with startingsolutions with protein contents in the range 5-20% (w/w). Proteinsolutions are frequently processed and atomised at these concentrationsas their viscosity properties (0.1-0.5 Pa.s (at a shear rate of 100 s⁻¹at 70° C. (Physica UDS200 rheometer, DIN double gap Z1 geometry) meanthat they are easily handled and pumped through standard processingequipment. Spray drying of solutions at the lower end of this proteinconcentration range can result in high levels of dusting (dustformation), which can result in reduced yields and increased risk ofdust explosions. An additional disadvantage of spray drying powders canbe the poor wettability and dispersibility properties of the driedpowders, which have a low density and tend to float on the surface ofwater-based liquids.

[0003] Powders produced by roller drying are characterized by higherdensities and improved wetting and dispersing properties. However, theseprotein powders have a less favourable taste profile, and have a darkercolour than their spray dried equivalents. These defects can be ascribedto the high protein concentration (around 40%) needed for an efficientroller drying process.

[0004] Lowering the solids or protein concentration in the roller dryingprocess to e.g. 20% (like in spray drying) would solve this problem.However, protein solutions in the 5-20% (w/w) concentration range do notlend themselves to roller drying. They become too fluid when applied tosteam heated rollers and spread to form too thin a film, which burnsonto the roller. The resulting film cannot be removed efficiently fromthe roller as a continuous film by the knives used for this purpose, butthe protein is rather removed as scorched dust. Alternatively, a double(twin) roller dryer type can be used in which the protein solutionsubject to drying is contained in a “pool” between the two roller drums.However, the long residence time in this pool at elevated temperaturescauses similar defects to the protein (browning) as observed in a highsolids single drum dryer process. Additionally, under these conditionsthe formation of lysinoalanine (LAL) may be favored, which is notdesirable.

[0005] It is therefore the object of the present invention to provide anew method of drying proteins, that obviates the above stated drawbacks.

[0006] This object is achieved according to the invention by a methodcomprising roller drying a protein solution having a relatively lowprotein content of less than 40% (w/w), preferably significantly lessthan 40% (w/w), wherein the proteins in the solution are crosslinked bycovalent bonds. The protein content is preferably 15-25% (w/w), morepreferably about 20% (w/w). These protein contents correspond to aviscosity in the range 1-10 Pa.s (double gap, Z1 geometry, shear rate100 s⁻¹ at 70° C.). It was surprisingly found that protein solutionshaving such relatively low protein content are still viscous enoughafter crosslinking to be suitable for roller drying. Roller drying is amuch simpler technique than spray drying and requires far lesscomplicated equipment. Therefore, malfunction or disturbance of theequipment is less likely to occur than in the case of spray drying.

[0007] In addition, no double drum dryer type is needed, since thesolution of this cross-linked protein preparation is now viscous enoughto be applied on a single drum dryer. This implies that no extrainvestment for a special drying technique is needed.

[0008] The proteins can be crosslinked in various ways. It is howeverpreferred that they are crosslinked by means of enzymatic treatment. Aparticularly suitable crosslinking enzyme is transglutaminase althoughothers such as peroxidases (such as lactoperoxidase, horse radishperoxidase or myeloperoxidase), laccases or mono amine oxidases are alsouseful. In addition, proteases can be used as crosslinking enzymes, whentheir peptidolytic action is reversed, which may be achieved underspecified conditions, known as the so-called ‘plastein’ reaction. Thecrosslinking is achieved prior to roller drying by exposing an amount ofprotein to an amount of crosslinking enzyme during an amount of reactiontime. For each protein suitable process conditions can be empiricallydefined. However, as a general rule the amount of protein is 5-30%(w/w), the amount of crosslinking enzyme is 0.01-20 units per gramprotein and the reaction time is 0.5-12 hours.

[0009] The specific activity of transglutaminase is determined using themethod as described by J. E. Folk and P. W. Cole, (1966), J. Biol.Chem., 241, 5518-5525.

[0010] The powder resulting from the method as claimed differs fromspray dried protein powders in that it is characterized by a higherdensity, improved wettability and dispersibility. The powder istherefore also part of this invention. A powder of the invention can becharacterised by means of its viscosity and microscopic analysis. Theviscosity of the product of the invention after redissolving the powderin water at 20% protein varies between 1 and 20 Pa.s. The differences inmicroscopic appearance between roller dried and spray dried powders canbe seen from FIGS. 5 and 6.

[0011] The powder of the invention can be used as a waterbinding agent,emulsifying agent, viscosity increasing agent, texture improving agent,stabilising agent.

[0012] The method of the invention can in principle be performed withall proteins that are susceptible to crosslinking by an appropriateenzyme. Examples of proteins that can be dried according to theinvention comprise milk proteins, such as casein and caseinates andenzymatic derivatives thereof, whey proteins, in particularα-lactalbumin, β-lactoglobulin and other animal proteins, such as eggwhite and blood or plasma proteins, vegetable proteins, such as soyproteins, rice proteins, potato proteins, and cereal proteins, such aswheat proteins, including gluten, glutenin, gliadin and soluble ordeamidated fractions thereof, corn proteins, including zein and solublefractions thereof, barley proteins, including hordeins and solublefractions thereof. It was found that the method is particularly suitablefor drying caseinate.

[0013] In order to control the drying process, the solution containingthe crosslinked protein can be heated to adjust the viscositytemporarily, as is normally done in drying operations. Preferably thisheating is to about 120° C. after which the solution is applied directlyto the rollers heated to approximately the same temperature.

[0014] The term “crosslinked protein(s)” as used in this application isintended to mean “at least two protein molecules having at least onecovalent bond between them”.

[0015] The present invention will be further illustrated in the examplesthat follow and which are in no way intended to limit the invention.

[0016] In the examples reference is made to the following figures:

[0017]FIG. 1: continuous protein film produced on a roller dryer with acrosslinked protein solution according to the invention;

[0018]FIG. 2: the same roller dryer as shown in FIG. 1 in which theviscosity of the crosslinked protein preparation is visible;

[0019]FIG. 3: discontinuous protein film produced on a roller dryer witha non-crosslinked protein solution;

[0020]FIG. 4: the same roller dryer as shown in FIG. 3 in which it isshown that the viscosity of the non-crosslinked protein preparation isinsufficient to keep the solution on the roller dryer drum;

[0021]FIG. 5: a microphoto of roller dried, crosslinked sodiumcaseinate; and

[0022]FIG. 6: a microphoto of spray dried sodium caseinate.

EXAMPLES Example 1

[0023] Roller Drying a Crosslinked Protein Solution

[0024] A solution of sodium caseinate (20% w/w; viscosity 300 mPa.s at70° C.) is reacted with the enzyme transglutaminase [E.C. 2.3.2.13]using 3 units of enzyme per gram caseinate for 1 hour at a temperatureof 50° C. The enzyme is deactivated by a heat treatment (90-120° C. for30 to 2 minutes, respectively). This treatment typically results in anincrease in viscosity from 0.1-0.5 Pa.s to 1-10 Pa.s at a shear rate of100 s⁻¹ at 70° C. (double gap Z1 geometry). viscosity measurements showthat the crosslinked caseinate solution has now shear-thinningproperties.

[0025] The crosslinked caseinate solution that has been treated todeactivate the enzyme activity is applied directly to the roller dryer(capacity 10-30 kg per hour) operating at a steam pressure of 2-3 barand a roller speed of 10-20 rpm. The roller drier is a pilot machine ofthe make “GMF”, equiped as a single drum drier. The drum has a diameterof 50 cm, and a length of 50 cm. Despite it's low protein concentration,an excellent protein film was formed on the drum, which could be removedefficiently by the built-in knives (FIGS. 1 and 2). The dried film isremoved by the built-in knives and fed to a milling machine and sieve.

[0026] The product thus obtained was redissolved in water to a solidscontent of 20% (w/w). The viscosity of the solution was measured underthe conditions described above and was 8.9 Pa.s. The micrograph of FIG.5 (Microscope: Wild M20, dispersion in xylol) shows the microscopiccharacteristics of a roller dried caseinate product according to theinvention, displaying particles of irregular shape, which show frayedends.

[0027]FIG. 6 shows for comparison a micrograph of spray dried sodiumcaseinate. The particles are so-called spray globules filled with airpockets.

Example 2 Comparative Example

[0028] A solution of sodium caseinate (20% w/w; viscosity 300 mpa.s at70° C., not crosslinked), is applied to the roller drier under the sameconditions as in example 1. The solution appears to be too thin to applyto the drum in a good manner (FIG. 4). A part of the applied feed poursoff the drum. The part of the feed solution that remains on the drumresults in a very thin, irregular and discontinuous dried film, showingopen patches (FIG. 3). The built in knives could merely remove thinpieces of film and dusty powder.

1. Method for preparing a dried protein preparation, comprising rollerdrying a protein solution having a relatively low protein content ofless than 40%, wherein the proteins in the solution are crosslinked bycovalent bonds.
 2. Method as claimed in claim 1, wherein the proteinsare crosslinked by means of enzymatic treatment.
 3. Method as claimed inclaim 2, wherein the enzyme is transglutaminase.
 4. Method as claimed inclaims 2 and 3, wherein prior to roller drying crosslinking is achievedby exposing an amount of protein to an amount of crosslinking enzymeduring an amount of reaction time.
 5. Method as claimed in claim 4,wherein the amount of protein is 5-30% (w/w), the amount of crosslinkingenzyme is 0.01-20 units per gram protein and the reaction time is 0.5-12hours.
 6. Method as claimed in claims 1-5, wherein the protein iscasein, caseinate, whey protein or a combination thereof.
 7. Method asclaimed in claim 6, wherein the amount of protein is 5-30% (w/w), theamount of crosslinking enzyme is about 0.01 units per gram of proteinand the reaction time is 0.5-12 hours.
 8. Method as claimed in claims1-7, wherein the protein content is 10-25%.
 9. Method as claimed inclaims 1-8, wherein the protein content is about 20%.
 10. Method asclaimed in claims 1-8, wherein the viscosity of the protein solution isin the range 1-10 Pa.s at a shear rate of 100 s⁻¹ at 70° C. measured ata Physica UDS200 rheometer with DIN double gap Z1 geometry or acomparable device.
 11. Protein powder, obtainable by a method as claimedin claims 1-10.
 12. Protein powder as claimed in claim 11, wherein theprotein is casein, caseinate, whey protein or a combination thereof. 13.Powder as claimed in claims 11 and 12 for use as a waterbinding agent,emulsifying agent, viscosity increasing agent, texture improving agent,stabilising agent.
 14. Use of a powder as claimed in claims 11 and 12 asa waterbinding agent, emulsifying agent, viscosity increasing agent,texture improving agent, stabilising agent.
 15. Use of a powder asclaimed in claims 11 and 12 as an ingredient in yoghurt or otherfermented milk products.
 16. Use of a powder as claimed in claims 11 and12 as an ingredient in meat products.